In general, an acrylonitrile-butadiene-styrene (hereinafter, called ‘ABS’)-based resin is widely used to electricity, electronic parts, office machines, car parts and the like due to its relatively good properties such as impact resistance, mechanical strength, moldability, gloss and the like.
As a method for preparing it, there is a method of conducting solution polymerization by dissolving rubber resin in monomer solution, or a method of preparing rubber latex using a diene-based monomer and conducting graft copolymerization by subjecting styrene and an acrylonitrile monomer to emulsion polymerization using thereof and the like. Commercially, the latter emulsion polymerization method is much used because it has advantages that it is easy to modify recipe according to quality level preferentially required and it can prepare various product families when extruding a product produced in the powder form and then mixing thereof with various matrix resins (PSAN, PC, PBT, PVC and the like) and additives (flame retardant, weather resistant stabilizer, antistatic agent, antibiotic and the like).
In preparing the ABS resin by this emulsion polymerization method, as mentioned above, the diene-based rubber latex is used to improve impact resistance. A commercially important part when preparing this diene-based rubber latex is i) an aspect of production efficiency and ii) securement of rubber latex properties (particle diameter, gel content) for effectively securing impact resistance of the ABS.
First of all, i) in the aspect of production efficiency, a general method for preparing a diene-based rubber latex has disadvantages that polymerization reaction should be usually conducted for 30 hours or longer to obtain large size, and polymerization conversion rate is little improved even though consuming more time because the polymerization conversion rate is rapidly reduced at the polymerization conversion rate of 90% or higher. In order to overcome this, in the case of conducting the polymerization under conditions of shorter reaction time and higher reaction temperature, there is a problem of reduced particle diameter and increased reaction coagulates, and also reaction pressure is increased by excess reaction heat thereby safety is low during mass production process. Thus, it is commercially difficult to obtain the large size polybutadiene latex having high conversion rate in a short reaction time.
Further, ii) in the securement of rubber latex properties for securing impact resistance of the ABS, particle diameter and gel content generated by internal cross-linking are largely recognized as important factors. For example, it is known that in general, in order to effectively secure impact resistance, the large-size rubber latex (3000 Å or higher) is more advantageous than small-size particle, and the rubber latex having lower gel content is more advantageous than the rubber latex having higher gel content. However, under the conditions of short reaction time and high conversion rate, the rubber latex having small particle diameter and high gel content is usually prepared. Thus, there are many difficulties in effectively securing rubber latex properties.
Accordingly, many companies are trying various methods for securing properties of the large-size rubber latex in consideration of productivity and properties.